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Commodore PET Question

Hugo Holden

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I'm thinking of buying a PET.

I have seen one where the front of the case says 3008, but the rear sticker says 2001-8 BS.

Three questions:

1) Why would it be that those model numbers are different or is that normal ?

2) Also I cannot see a DIN connector on the rear panel for a 1541 disk drive, is that because this model is too old to support that drive or is an adapter pcb required ?

3) If it cannot interface with the 1541 disk drive, what would be the first PET model that did and had the DIN connector ?

Thank you for any advice on PETs.
 

daver2

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Hi Hugo - you have finally been seduced!

The 2001N / 3000 era is a bit 'muddy' to say the least. If you look on the Zimmers Commodore PET website you will see that the 2001N, 3000 and 4000 series are all lumped together.

In repairs, I have seen all sorts - with bits and pieces from one type of PET in another. I don't think this is an 'aftermarket' repair - but something that Commodore may have done in the factory to either ship PETs out of the factory door - or to deplete stocks of parts. I am not sure what is true though - I am guessing.

From my recollection, a Commodore PET never supported the DIN-connector type of Disk drive. The preferred method was the IEEE 488 interface.

Dave
 

VERAULT

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the din style serial connector didnt come out until the Vic20. your choices were ieee488 drives only. you can get yourself a petSD+

I was lucky enough to find an 8250 dual floppy drive. one drive works at the moment. My first ieee488 drive was the sfd1001. the upper head failed (like most of those drives) so i need to disable that head to use the drive. alot of those drives need alot of work so its easier to use an SD option unless you really want one
 

Hugo Holden

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From my recollection, a Commodore PET never supported the DIN-connector type of Disk drive. The preferred method was the IEEE 488 interface.

Dave

Hi Dave,

Is there an adapter pcb design that can allow the PET to work with a Din connector drive ? I have a couple of good 1541 drives and was wondering if these could work with a PET, probably not by the sound of it.

Also I figured if I got a PET I could be in a better position to suggest tests and repairs on the VDU etc.
 

robert_sissco

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I don't think there ever was a mainstream adaptor, although I have a feeling that there might be some who have made some either as a hardware hack, or in small runs. So if there were any, they may cost as much as the PET itself. Even the disk drives that were made for it are rather rare, and most I have seen have gone for hundreds of dollars and usually listed as "For parts or repair".

I love my 1571 for my VIC and C64, but I am more than happy to use a SD2PET for my PET
 

Eudimorphodon

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Re: using a 1541 on a PET, so far as I'm aware there isn't an IEC host board for Commodore PETs, but there do exist hacks to add a parallel IEEE-488 port to a 1541 drive. (Essentially converting it into the rare "2031LP".) Here is the github for a modern version of the necessary circuit and ROM patches. If you don't want to deal with a CPLD then it might be possible to follow the directions to recreate one of the older versions of it. (The idea originally appeared in a Commodore magazine in the 1980's.)

Honestly, though, it seems like a lot to go through just to use a device that might not have very much of its original magic smoke left. Using a modern flash device instead will make your life easy.
In repairs, I have seen all sorts - with bits and pieces from one type of PET in another. I don't think this is an 'aftermarket' repair - but something that Commodore may have done in the factory to either ship PETs out of the factory door - or to deplete stocks of parts. I am not sure what is true though - I am guessing

I firmly believe the evidence supports the idea that Commodore at times just grabbed parts out of whatever bins had pieces in them and shoved the machines out the door. This especially applies if the machine was part of a bulk order for education.

Basically there are four "main" types of PETs:
  • The original chicklet keyboard models
    • Usually say they're a "2001" if they have a number, the labels vary a lot.
    • These *probably* all came with one of several different motherboard variations that held a maximum of 8K of static RAM. I say "probably" because my chicklet model came with an 8k "Dynamic Board" (see below) in it, but it also had a "REFURBISHED" sticker on the back.
    • If one of these has a blue monitor bezel you'll probably pay through the nose for it.
    • Will have BASIC version 1 (buggy) or 2
  • 40 column 9-inch machines with the "Dynamic Board"
    • May carry any of a bewilderingly large range of model numbers, from "2001-N" through "4032"
    • Will have BASIC versions 2 through 4. (I think 3 is vanishingly rare in the wild.) The first digit of the model number slapped on it *may* correspond with the BASIC version it shipped with, but don't count on it.
    • System board holds up to 32k of dynamic RAM in two banks; 8K (and maybe some 16k?) machines may have holes drilled in the PCB to disable the use of one of the two banks in a sad effort to prevent user upgrades. (My "REFURB" 2001 has a drilled board.)
    • The "Dynamic Board" doesn't have a CRTC, which means it's safe from the "killer poke"... although a refurbished 9" *could* have the "Universal" board (see below), it was possible to configure it as a replacement for the Dynamic board, which means it *would* be susceptible.
  • 40 column 12" machines with the "Universal" board.
    • Model number is usually in the 4000s. (4008-4032) Confusingly there are 9" machines with the same model numbers.
    • The "Universal" board was used in both 40 and 80 column PETs; a combination of the installed ROM, amount of installed VRAM, and a mess of jumpers determines its "personality".
    • So far as I know they're all BASIC 4.0
    • These are the ones that can be "Killer Poked"
  • 80 column machines.
    • If its model number is 8032 or less is probably a "Universal" board (or a predecessor that's basically the same but hardwired to 80 column mode), otherwise may use a more specialized board with a memory daughterboard.
    • Probably not what a casual user wants today because they're less compatible with "fun" software than 40 column machines.
My favorite is probably the "Dynamic" board models because they're the simplest to repair today, but a deep pet hacker probably would enjoy a Universal board with some add-ons to allow it to switch personalities.
 

Hugo Holden

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  • System board holds up to 32k of dynamic RAM in two banks; 8K (and maybe some 16k?) machines may have holes drilled in the PCB to disable the use of one of the two banks in a sad effort to prevent user upgrades. (My "REFURB" 2001 has a drilled board.)
That is very interesting. I totally disagree with such vandalism and if its from a manufacturer, that is inexcusable.

Is the pcb in these PETs a 2 layer or a 4 layer board ?

If its a 2 layer it should be ok to repair it easily, but a 4 layer more tricky, but should be ok with the schematic and added link wires.

The term Dynamic Board, does this mean that the RAM on them is dynamic RAM ?
Can they be fitted with Static Ram ?
 

daver2

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You can see some typical ’vandalisation’ here: https://retrocomputing.stackexchange.com/questions/16483/cbm-pet-2001-garbled-screen

The PET boards are two layer, so yes - repairable if you do want to expand the memory on a machine if you buy a lower specification machine if the unused RAM locations have been butchered! If not drilled out, the IC pin mounting holes may all be filled with solder.

Commodore eventually gave up with this practice... Therefore, more earlier (and perhaps more desirable) specimens, could have this vandalism. Something to be aware of when buying - and you may be able to use it as a tactic to reduce the price you pay if you are a buyer.

The 2001 used static memory. The 2001N onwards used dynamic memory. The earlier machines came with 4K chips (so had a capacity of 4K or 8K) whilst the later machines came with 16K chips (so 16K or 32K). You could also be able to replace the 4K chips with 16K chips. There would be a few link changes to accommodate this modification.

If I remember correctly, all of the dynamic RAM PETs could use 4K or 16K chips, but the later Universal 2 removed the capability to use 4K chips.

I used both the very first chicklet keyboard and the 8032 at university. I have an 8032 at home, but aspire to obtain a 9” screen chicklet machine at some point in the future. I think the ‘proportions’ of the 9” machine “looks right”, but the 12” screen looks too big (aesthetically). That’s just my view though...

Dave
 
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Eudimorphodon

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If I remember correctly, all of the dynamic RAM PETs could use 4K or 16K chips, but the later Universal 2 removed the capability to use 4K chips.
Actually I don’t think they do support 4K DRAMs, which is a little confusing since “8k” was an available configuration. What they did for that is use 4108 “8kbit” DRAMs; 8k in quotes because those chips were in fact half-bad 16k chips. (The datasheet for those chips is pretty transparent about it; they even came in two SKUs depending on which half the bad bit was in so you’d know to hold the associated address line constantly high or low for that bank.) My drilled board actually has 16k in it now because enough of the 4008s were bad it didn’t make sense to keep any of them.

(The manual for the dynamic board lists two different options for configuring 16k, either one bank of 16k chips or two of the 8ks. I’m curious how common the latter was.)

I’ve heard that Commodore also sabotaged Static boards with 4K installed, but I don’t know that I’ve seen one.
 

Hugo Holden

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This is the most disgraceful thing I have seen any manufacturer do, had to be an idea from management, I cannot believe that any technician would have thought this up or agreed with it.

If I was tasked with fixing this, I would smooth out the edge of the hole. Have manufactured some discs of pcb with the exact size and correct tracks and pads, glue them in flush with 24hr epoxy resin and rotate then to the correct alignment and bridge the track edges with solder. Likely each disc would be a custom one as the holes might not be in exactly the same position in each case. Attached close up of the holes.

The computer I was looking at on ebay UK, unfortunately does not have the photo of the pcb; but it looks good cosmetically:

 

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VERAULT

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Yeah there holes in the PET is board is pretty well documented. IT does seem like an extreme length to go to to force memory variations on a customer.
 

daver2

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I agree Hugo. It was a 'bodger' with a drill!

That looks a nice PET you are bidding on... Good luck.

Dave
 

Eudimorphodon

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The computer I was looking at on ebay UK, unfortunately does not have the photo of the pcb; but it looks good cosmetically:

The shot of the BASIC prompt says it has 32K; that’s inconsistent with the “3008” label since that should indicate an 8k model, but it is of course good news since it means it’s already upgraded. (Granted there are multiple possibilities *how*, it *could* have a drilled board worked around with a daughter board, but more likely not.)
 

Eudimorphodon

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… re: fixing the dead bank on a drilled one, if the priority was just to “make it go” instead of look good I’d probably consider piggybacking for the second bank of RAM. I don’t have the board layout in front of me but I think that could work with just running the other CAS line to the piggybacked chips.
 

Hugo Holden

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The shot of the BASIC prompt says it has 32K; that’s inconsistent with the “3008” label since that should indicate an 8k model, but it is of course good news since it means it’s already upgraded. (Granted there are multiple possibilities *how*, it *could* have a drilled board worked around with a daughter board, but more likely not.)
Interesting info. To some extent the fact that it is working kind of worries me, that somebody has recently been working on it. I like to do all the hardware repairs myself as I'm very fussy. I don't mind if there are naturally occurring faults as I find most fun to locate and repair. The human induced ones are another story.
 

Hugo Holden

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Good Lord, I won the Auction.

And thank the Lord I have the good people here on the forum to help me with the software side of the machine, I'm ok on the hardware side of things, but not so much the software, where I tend to struggle a lot.
 

daver2

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Hugo,

Well done on winning the auction.

We’ll have to teach you a bit about the software then...

Dave
 
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